Filtering tweets by hashtag
You can tag a post with a particular topic by including in the tweet the topic word preceded by the hash symbol (#). For example, if you post a tweet related to Microsoft’s Windows 7 operating system, you could include the hashtag #windows7 somewhere in the tweet. However, the real purpose behind hashtagging tweets is that they give you and other tweeters an easy way to search for a particular topic because the hashtag acts as a kind of natural filter.
Here’s how to perform a hashtag search using the Advanced Search page:
1. Click Advanced Search in any search page. The Advanced Search form appears.
2. In the This Hashtag text box, type the hashtag topic you want to find. Don’t add the
hash (#) in front of the topic word; Twitter adds it for you automatically.
3. Click Search. You see a list of tweets that include the hashtag.
Hashtag searching is probably easiest from the Search box because all you have to do is place the hashtag operator (#) in front of the topic. For example, figure 6.18 shows a search for the hashtag #windows7 where the tweet also includes the sad emoticon.
Reference : wiley.com